The present invention relates to a method for restoring punch and die alignment of a turret-type punch press machine and a cutting tool and sleeve insert for use in the method.
A well known type of punch press machine includes an upper circular turret and a lower circular turret, both co-axially mounted for rotation about a common axis of rotation and each having a plurality of angularly spaced apertures. The apertures of the upper turret each support a punch holder in which a punch is supported for axial movement. The apertures of the lower turret each support a die (which is typically supported on a die holder mounted at the aperture). An axially movable ram is disposed above the upper turret at the same radial spacing as the upper turret apertures and is operable to reciprocally axially move a punch holder supported at a respective upper turret aperture into punching engagement with a workpiece supported on a die of the lower turret aligned with the punch.
A punching operation thus requires alignment among the respective die of the lower turret, the respective punch of the upper turret, and the ram. However, several commonly occurring conditions combine to degrade this alignment and thereby impair the efficiency of the punch press machine. Each upper turret aperture typically includes a radially movable, spring biased pin which maintains the punch holder in its topmost position within the aperture. The axial movement of the punch holder cyclically applies a radial force to the pin, whereupon the spring biasing force increases to a relatively marked degree, and the portion opposite of the aperture in which the spring biased pin is disposed is subjected to considerable wear.
The axial motion of the punch holder also imparts wear forces on the aperture. Also, when a punch operation involves "nibbling"--e.g., the progressive punching of a workpiece to make a larger hole therein--wear occurs randomly on the surface of the punch holder and this contributes to wear on the aperture. Moreover, on punch press machines equipped for plasma torch burning of large holes, a by-product of such burning is the accumulation of a significant amount of slag of a highly abrasive nature. The slag, as well as oil or other lubricant on the top of the turret, tends to flow into the aperture in the space between the punch holder and the walls of the aperture, whereupon the rate of wear of the aperture is accelerated.
Yet a further reason for wear on the aperture of a turret is imprecise engagement of a turret by an assembly which maintains the turret at a predetermined angular position in which the respective punch supported by the turret is aligned with the ram. Typically, such an assembly includes a pressurized cylinder-actuated index pin which is extended radially inwardly toward the turret to engage a corresponding index aperture in the circumferential surface of the turret. If the respective circumferential aperture of the turret is not precisely aligned with the index pin when the pin is driven radially inwardly, the index pin is not inserted cleanly into the circumferential aperture but is, instead, driven with relatively significant side thrust force against the turret. This produces a backlash force on the pressurized cylinder supporting the index pin and leads to a loosening of the mounting of the pressurized cylinder on the machine frame. Thus, while it is possible for an index pin to still engage a circumferential aperture to thereby maintain the turret in a fixed angular position, the loosened condition of the pressurized cylinder, as well as wear on the circumferential aperture, leads to angular misalignment among the ram, punch and die. Typically, the upper turret is more massive than the lower turret and correspondingly larger force is required to precisely position the upper turret, whereby the severity of angular misalignment due to a loosened pressurized index pin cylinder is more pronounced with respect to the upper turret and its associated index pin assembly than the lower turret. Accordingly, the need exists for a method for efficiently and precisely restoring the punch and die alignment of a punch press machine.